1. Field of the Invention
The present invention relates generally to a mechanical seal device. More particularly, the invention relates to a mechanical seal device disposed at the end portion of a housing of large pumps, agitators or the like which provides a seal against a sealed process fluid between the housing and a rotary shaft whose pressure ranges from a low pressure to a high pressure.
2. Description of the Related Art
There has been a mechanical seal device for a high pressure pump as a relative art of the present invention, for example being disclosed in U.S. Pat. No. 5,114,163. However, this mechanical seal device is likely to impose a higher cost for individual seal elements as they require relatively large dimensions. This is a first problem which needs improvement. In addition, the seal device is so constructed that a rotary seal ring and a stationary seal ring receive the pressure from the sealed process fluid in the same direction. Therefore, when the fluid pressure is increased, a high pressure is exerted in the same direction to both the rotary seal ring and the stationary seal ring. Under this circumstance, if an excessive pressure is exerted by the sealed fluid against the rotary seal ring, there is a chance that the rotary seal face departs from the mating stationary seal face, which will cause a breakage of a sealing contact. This is a second problem to be solved. There remains another problem yet to be resolved. That is, the rotary seal ring is fixed relative to the rotary shaft while the stationary seal ring is fitted to the housing. Therefore, a thermal expansion of the rotary shaft not only may hamper a sealing contact between the stationary seal face and the rotary seal face but also is likely to cause unwanted eccentricity.
FIG. 3 represents a mechanical seal device 200 as an example of the above mentioned relative art, which will be described in details below. The mechanical seal 200 in FIG. 3 is formed and dimensioned in a large size due to its deployment over a rotary shaft 148 which itself is large in diameter, which leads to a heavy weight of the entire seal assembly. Therefore, the mechanical seal device is typically divided into two split parts so that deployment of the seal device to the rotary shaft 148 is simplified.
This split-type mechanical seal 200 provides a seal against the sealed process fluid between a housing 150 and the rotary shaft 148 at a pair of mating seal faces, i.e., a stationary seal face 161 of a stationary seal ring 160 and a rotary seal face 171 of a rotary seal ring 170, whether the seal faces are subject to a relative sliding motion or remain stationary.
There is a clearance between an inner surface of the stationary seal ring 160 and the rotary shaft 148 through which the sealed process fluid reaches a second gland 175 which is located closer to the rotary seal ring 170.
A first gland 165 has a thick annular structure whose half cross section is shaped like an alphabet character L. An outer diameter surface of the stationary seal ring 160 is securely fitted with an inner diameter surface 167 of a cylindrically extending portion of the first gland 165. A flange section 166 which is disposed at the other end of the cylindrically extending portion of the first gland 165 makes a sealing contact with the end surface of the housing 150.
The first gland 165 is fixed to the inner diameter surface of the split stationary holder 168 which consists of two split pieces. The other end portion of the split stationary holder 168 is fixedly mounted on a protruding portion which is located at one end of the housing 150.
The split stationary holder 168 fixedly retains the stationary seal ring 160 with the first gland 165 being disposed therebetween. The stationary seal ring 160 and the first gland 165 are retained within the split stationary holder 168 and are fixated by means of clamping screw bolts 153, 153.
As the first gland 165 covers the entire inner surface of the split stationary holder 168, a flange section 166 of the gland between the stationary seal ring 160 and the housing 150 is made to have a thick wall so as to sustain a high pressure. Therefore, the first gland 165 tends to be large in size and heavy in weight. In addition, a forming die for the first gland 165 incurs a high manufacturing cost. These are problems to be resolved.
The rotary seal ring 170 forms a loose fit relative to the rotary shaft 148 with a clearance therebetween and the rotary seal face 171 makes a sealing contact with the stationary seal face 161 for providing a fluid tight seal against the sealed fluid even under a relative sliding movement. Outer diameter surface of the rotary seal ring 170 is fitted to an inner diameter surface 177 of the second gland 175. Also the rotary seal ring 170 is securely fixed to the split rotary holder 178 via the second gland 175. As this second gland 175 is large in diameter, a forming die for it results in a high manufacturing cost. Furthermore, different forms of the first gland 165 and the second gland 175 necessitate use of different forming dies, which even further increases the total manufacturing cost. This is another problem yet to be accommodated.
Split rotary holder 178 is fixed to the rotary shaft 148 by means of a key which does not appear in the figure. The split rotary holder 178 is assembled as an integral unit by fastening a couple of screw bolts 154, 154 at a pair of mating surfaces. Therefore, the large-in-diameter cylindrical portion of the second gland 175 provides a seal between the rotary seal ring 170 and the inner surface of the split rotary holder 178. Likewise, a small-in-diameter cylindrical portion of the second gland 175 provides a seal between the rotary shaft 148 and the split rotary holder 178. These two cylindrical portions both of which are shaped in a thick wall make it difficult to achieve a sensitive pressure control at the mating faces even with the screw bolts being tightly fastened, which is prone to a leakage of the sealed process fluid. This presents another problem to be remedied.
The second gland 175 thus formed makes the split rotary holder 178 heavy as well. Rotating the split rotary holder 178 with the rotary shaft 148 tends to cause an eccentricity of the rotary shaft 148, and such an eccentricity in turn causes abrasions of the rotary seal face 171 of the rotary seal ring 170 as well as of the stationary seal face 161 of the stationary seal ring 160. This imposes a further problem.
In a mechanical seal device thus constructed, the flange portion 166 of the first gland 165 located between the split stationary holder 168 and the end face of the housing 150 is necessarily shaped in a thick wall so as to achieve a seal contact at the stationary seal face 161 and the rotary seal face 171, and so is the radially extending portion of the second gland 175. This is another problem to be improved.
The stationary seal ring 160 is fixated relative to the housing 150 via the split stationary holder 168 while the rotary seal ring 170 is fixedly secured to the rotary shaft 148 via the split rotary holder 178. If the rotary shaft 148 is subject to a thermal expansion in its outward and axial direction, the seal contact between the stationary seal face 161 and the rotary seal face 171 is disturbed. This creates another problem to be solved.
The present invention is introduced to resolve the above mentioned problems. A primary technical goal which this invention tries to achieve is to improve a seal performance of a mechanical seal device such that a pair of seal faces which are mutually in contact are able to maintain a fluid tight seal even under a great pressure or varying pressure of a sealed process fluid.
Another goal is to fixate a rotary seal ring relative to a rotary shaft by integrating with a diaphragm in the outside of a housing such that a good seal performance is exhibited even under a great pressure or varying pressure of a sealed process fluid or when the rotary shaft is bent.
Yet another goal is to decrease the manufacturing cost of parts involved in the mechanical seal device, to simplify assembly of the parts, and to reduce the total manufacturing cost of the mechanical seal device as a whole.